Mystery of complementary topology in VCO design
时间：04-09
整理：3721RD
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Dear all:
I am designing a VCO circuit using cross-coupled structure and a PN performance of -80dBc/Hz@10K offset is required. I encountered some problems that violate the theory i've studied from many papers.
As i know from my study, using complementary topology can get better PN performance due to its larger amplitude at the same bias current compared to PMOS-noly or NMOS-only topologies.
Unfortunately, when I use complementary topology, the PN is really bad no matter how hard i tried to optimize my design..(about -60dBc/Hz@10K), but while i use NMOS-only topology, i can get good PN easily(about -85dBc/Hz), this result really confused me....is there anything special that should be noticed while using complementary topology?
I am designing a VCO circuit using cross-coupled structure and a PN performance of -80dBc/Hz@10K offset is required. I encountered some problems that violate the theory i've studied from many papers.
As i know from my study, using complementary topology can get better PN performance due to its larger amplitude at the same bias current compared to PMOS-noly or NMOS-only topologies.
Unfortunately, when I use complementary topology, the PN is really bad no matter how hard i tried to optimize my design..(about -60dBc/Hz@10K), but while i use NMOS-only topology, i can get good PN easily(about -85dBc/Hz), this result really confused me....is there anything special that should be noticed while using complementary topology?